A halide scintillator for radiation detection is described in U.S. Published Patent Application No. 2011/0272585 and a chloride scintillator for radiation detection is described in U.S. Published Application No. 2011/0272586 published Nov. 10, 2011, both published applications of Zhuravleva et al. of the University of Tennessee. The halide scintillator is single-crystalline and has a composition of the formula A3MBr6(1-x)Cl6x or AM2Br7(1-x)Cl7x wherein A consists of one of Li, Na, K, Rb, Cs or any combination thereof, and M consists of Ce, Sc, Y, La, Lu, Gd, Pr, Tb, Yb, Nd or any combination thereof and 0≦x≦1. The chloride scintillator is also single crystalline and has a composition of the formula AM2Cl7 and A and M consist of the elements indicated above. A modified Bridgman technique was used to form the crystals. A Bridgman method is described in Robertson J. M., 1986, Crystal Growth of Ceramics: Bridgman-Stockbarger method in Bever: 1986 “Encyclopedia of Materials Science and Engineering,” Pergamon, Oxford pp. 963-964” among other known tutorials incorporated by reference herein as to any material deemed essential to an understanding of the Bridgman method.
An iodide scintillator for radiation detection is described in EP 2387040 published Nov. 16, 2011 and claims priority to U.S. patent application Ser. No. 13/098,654 filed May 2, 2011 and to U.S. provisional patent application Ser. No. 61/332,945 filed May 10, 2010, also of Zhuravleva et al. of the University of Tennessee. The disclosed iodide scintillators have a composition of the formula AM1-xEuI3, A3M1-xEuxI5 and AM2(1-x)Eu2xI5, wherein A consists essentially of an alkali element (such as Li, Na, K, Rb, Cs) or any combination thereof, M consists essentially of Sr, Ca, Ba or any combination thereof, and 0≦x≦1. These iodide scintillator crystals were made by first synthesizing a compound of the above composition and then forming a single crystal from the synthesized compound, for example, by the Vertical Gradient Freeze method. In particular, high-purity starting iodides (such as CsI, SrI2, EuI2 and rare-earth iodide(s)) are handled in a glove box with, for example, pure nitrogen atmosphere and then mixed and melted to synthesize a compound of the desired composition of the scintillator material. A single crystal of the scintillator material is then grown from the synthesized compound by the Bridgman method or Vertical Gradient Freeze (VGF) method, in which a sealed ampoule containing the synthesized compound is transported from a hot zone to a cold zone through a controlled temperature gradient at high speed to form the single-crystalline scintillator from molten synthesized compound. The ampoule may be sealed with a hydrogen torch after creating a vacuum on the order of 1×10−6 millibars. The scintillator crystal may be cut and polished using sand papers and mineral oil and then optically coupled to a photon detector, such as a photomultiplier tube (PMT), arranged to receive the photons generated by the scintillator and adapted to generate a signal indicative of the photon generation. Typically, plates about 1-3 mm in thickness may be cut from the boules and small samples selected for the optical characterization. This scintillator crystal work has been continuing at the University of Tennessee, Scintillation Materials Research Center, Knoxville, Tenn.
Also, pursuant to U.S. Published Patent Application No. 2011/0165422, published Jul. 7, 2011, complimentary development of a lanthanide doped strontium barium mixed halide scintillator crystal, for example, Sr0.2Ba0.75Eu0.05BrI has been developed with 5% Eu doping, also using a Bridgman growth technique, at the University of California.
Pursuant to U.S. Published Patent Application No. 2011/0024635 published Feb. 3, 2011, of Shah et al., a lithium containing halide scintillator composition is disclosed. This CsLiLn composition appears to have been produced at Radiation Monitoring Devices, Inc. of Watertown, Mass.
The need for radiation detecting materials has been at the forefront of materials research in recent years due to applications in national security, medical imaging, X-ray detection, gamma-ray detection, oil well logging (geological applications) and high energy physics among other applications. Typically, a crystal of the types described above desirably exhibit high light yields, fast luminescence decay (for example, below 1000 ns), good stopping power, high density, good energy resolution, ease of growth, proportionality and stability under ambient conditions. LaxBr3:Ce1-x (E. V. D. van Loef et al., Applied Physics Letters, 2007, 79, 1573) and SrxI2:Eu1-x (N. Cherepy et al., Applied Physics Letters, 2007, 92, 083508) are present day benchmark materials that satisfy some of the desired criteria, but their application is limited due to the extreme hygroscopic nature. Other known benchmarks that are commercially available include bismuth germanate (BGO) and NaI:Tl available from a number of sources.
There remains a need in the art for further research and development of scintillator crystal materials for the applications described above.